The sugar acts as nutrient needed for the growth of bacteria, which can deteriorate the wine or even turn it into grape vinegar.

[4] During the brewing process, microbial spoilage can lead to the deterioration of wine quality and taste, making it unhygienic and unacceptable to consumers.

[5] In addition, microbial diseases of wine are mainly caused by yeast, lactobacillus and acetic acid bacteria.

[6] This is because yeast may re-ferment a wine with high sugar content, making it cloudy and impure.

[3] Tannins, also known as polyphenols, are found in the xylem, bark, leaves, fruits and roots of plants.

[4] Acid protects wine from bacteria by regulating the pH value, which affects the growth and vitality of yeast during fermentation.

Sorbic acid, which acts like sulfites, has recently been approved for use in European Community countries, but only under very limited conditions.

[11] Apart from sulfur dioxide, which is used most frequently, other chemicals such as benzoic acid, diethyl pyrocarbonate, parabens, pimaricin and sorbic acid are also used as preservatives in wine, but the potential threat or side effects of these chemicals are still to be investigated, so they are not permitted to be used in large quantities for the time being.

[10] Compared with other preservatives, weak acids are characterized by their antiseptic effect by slowing down the growth and reproduction cycle of microorganisms rather than killing them.

Sulfites, or small molecules of sulfur dioxide (SO2) and hydrogen disulfide (H2O2), are commonly used as preservatives in wine and even other fruit drinks.

[7] Their principle is basically to make microbial protein coagulation or denaturation, thereby interfering with their growth and reproduction.

[4] Studies have shown that a possible cause of allergy in wine ingredients is an adverse reaction to sulfur dioxide by asthma patients.

[16] Because of the controversy, disease-causing preservatives have been used as sparingly as possible[16] or clearly labeled on wine bottles to make it easier for people with the disease to stay informed.

[13] In addition, researchers have targeted potential biological preservatives, such as antimicrobial peptides and bacteriolytic enzymes.

[5] It has been reported that many food preservatives, including sorbitan, hydrogen peroxide, benzoic acid and sodium benzoate, can cause health problems, especially in high doses.

[16] In addition, as mentioned in the controversy section, the adverse effects of sulfites on asthma patients also confirmed the health threat of preservatives containing this substance.

[17] But the possibility of adding antibacterial compounds to the manufacturing process may prevent the risk from being completely avoided, so the study is ongoing.